Woznaldo: you really should start your own thread as your issue is separate from the OPs who was specifically looking for information about free video converters where you're looking for assistance with a specific video converter.
I've never used Prism before, but conversion will depend on how long the video is, what your settings are, quality of the conversion software and of course the system itself (ie: CPU model and speed, RAM, etc.).
Longer the video is (not necessarily the larger the file size) will take longer to transcode, the bigger the change in the video (ie: resizing from HD to say a resolution for an iPod Touch) will take longer to transcode, depending on the capabilities of your hardware, when going from one codec to another (possibly more difficult codec) can add time to your transcode, if you've pegged all cores on your machine and it's taking forever to transcode then either try different software that may be more efficient or understand that your system just can't go any faster with the given software package (you can check your activity monitor while transcoding or look for an older version of iStat Menus (they just went to pay for with version 3.0) to watch your CPU activity.)